1. Field of the Invention
This invention relates to the handling of wafers, and more particularly to the handling of wafers in a wafer testing and/or processing procedure and apparatus.
2. Background of the Related Art
The manufacture of integrated circuits (I.C.'s) begins with blank, unpatterned semiconductor wafers. These wafers undergo a number of sometimes critical process steps before being formed into the final I.C. form. A substandard wafer can affect the number of usable I.C.'s on a wafer (yield). It is therefore desirable to have a machine for testing wafers to ensure the wafers meet a customer's standards to maximize wafer yield.
The testing of wafers is often accomplished by an automated process, in which robots continuously handle and test the wafers. Robot testing and handling tends to be more efficient than manual testing and handling of wafers, since robots can be much faster, more precise, and less contaminating than human operators when handling wafers. In wafer handling processes, wafers are typically transported using carriers such as wafer cassettes and wafer pods. Pods differ from cassettes in that the pods typically are sealed to prevent contamination to the wafers enclosed therein.
Previously, wafers having a diameter of 8 inches were commonly used in the semiconductor industry for the manufacture of I.C.'s. More recently, 300 mm or 12-inch diameter wafers have been introduced to allow a greater number of integrated circuits to be produced from one wafer, thus lowering the cost of producing the I.C.'s. New equipment and procedures have been developed to handle and process these new, larger wafers. For example, new larger, standard wafer pods, or Front Opening Unified Pods (FOUPs) have been developed. These sealed pods provide a contamination-free storage environment for the wafers. To unload the wafers, the FOUP is positioned so that the wafers are oriented horizontally, the front door of the FOUP is opened to a contamination-free environment inside the testing equipment and a robot end-effector is used to remove a wafer for processing or testing. Other versions of pods are used for smaller sized wafers; for example, Standard Mechanical Interface (SMIF) pods are typically used for 5-inch, 6-inch, and 8-inch wafers.
One tool for use with contamination-free handling of wafers is a load port. These tools allow a wafer carrier or pod to dock to a handling tool while providing a continuous, clean environment for wafers as they are unloaded from the FOUP by the end-effector mechanism. One typical example of a prior art load port is illustrated in FIGS. 1a-1c. In FIG. 1a, load port mechanism 10 includes a panel 11 having an equipment side 12 and a FOUP side 14. On the FOUP side 14 of panel 11, a FOUP 16 is positioned on an unloading station 18 and includes one or more wafers. In some embodiments of load port mechanisms, additionals FOUPs can be loaded in the mechanism 10 and can each be moved into the unloading position once the wafers of FOUP 16 have been unloaded, processed and/or tested.
On the equipment side 12 of panel 11, the load port mechanism 10 includes a opening 22 in panel 11 which is approximately the same dimensions as a front door 24 of the FOUP 16. The front door 24 is aligned with the opening 22, where contamination is prevented from entering the clean environment by exerting positive air pressure inside the clean environment. Front door 24 includes several fastening mechanisms 26, such as registration pins, latch keys, vacuum fasteners, and, optionally, purge ports for the introduction/withdrawal of gasses from the FOUP 16.
Load port mechanism 10 also includes a door removing mechanism 30, which includes a plate 32 and a support rod 34. The plate 32 and rod 34 are shown in a lowered position in FIG. 1a. FIG. 1b illustrates the load port mechanism 10 of FIG. 1a in which the door removing mechanism 30 has been moved into a position to remove the front door 24 of the FOUP 16. Plate 32 has been raised by support rod 34 by motors or other mechanism to the level of door 24 and opening 22. The plate 32 and rod 34 are then moved toward the opening 22 and plate 32 is inserted into the opening to engage the door 24. Preferably, plate 32 includes components that mate with the fastening mechanisms 26 on the front door; e.g., plate 32 can include apertures into which pins on door 24 fit, latch keys to unlock a latch securing the door, etc. In some embodiments, vacuum pressure can be used to assist the plate 32 in mating with door 24.
FIG. 1c illustrates the prior art load port mechanism 10 after door removing mechanism 30 has removed the front door 24 from the FOUP 16. The plate 32 and rod 34 is moved back three or more inches from the inserted position of FIG. 1b, where the door 24 is attached to plate 32. The plate and door are then lowered to the position shown in FIG. 1c. Since the wafers in FOUP 16 now are accessible through opening 22, a robot having z-axis movement such as handler arm 34 and end-effector 36 can be used to remove one or more wafers, one at a time, and transport the wafers to another testing or processing station. The FOUP 16 remains stationary as the robot is moved to different elevations to take out the wafers. The robot loads the wafers into the FOUP in the same way that the wafers are unloaded after the wafers have been tested and/or processed. In some embodiments, a can be lowered to the unloading position once the wafers of FOUP 16 are tested or processed.
While the prior art wafer handling and test systems have been successful in handling and testing wafers, they tend to exhibit some undesirable characteristics. One problem with the load port mechanism as illustrated in FIGS. 1a-1c is that the mechanism is dedicated to one size of FOUP. For example, 300 mm wafer FOUPs are typically provided as two standard sizes: a smaller size that holds 13 wafers and a larger size that holds 25 wafers. The opening 22 of the prior art load port mechanism has a single size intended to fit one side of FOUP door; thus, to fit a different sized FOUP door, the frame having opening 22 must be changed to a different frame having the desired size of opening, and plate 32 must be changed to one having the appropriate size. Making these complex mechanical changes can take hours, and the contaminant-free air of the processing environment must be broken, requiring the environment to be cleaned again after the change is made.
Another problem with the prior art load port mechanism is that the cost of the mechanism can be excessive. A robot mechanism is required to unload the wafers from the FOUP, and the robot must have several degrees of freedom to access the wafers of the FOUP, including a fairly large z-axis movement. This requires a more complex and costly type of robot that requires more maintenance, which is undesirable in production environments. In addition, the load port mechanism of the prior art must elevate a plate 32 by ten or more inches and then move the plate toward the door of the FOUP by a distance of three or more inches. A mechanism providing such movement is more expensive than simpler mechanisms having less degrees of freedom and moving the components a shorter distance.